Cyclone III configuration

FvM, it is very difficult to understand you. You should break up your sentences into smaller ones. (I learned recently that German has special features to build up very complex sentences. However, in English doing that is usually a very bad idea, especially if you're not a good speaker.)

"I can't see, that the Terrasic variant is generally superior to Altera, I could also report an example where only Altera is working correctly and a customer, who uses a ESD protection circuit for JTAG interface in all designs never had any JTAG problems, with either Altera or Terrasic Blaster."

Do you mean to say that one customer had problems with the Terrasic cable, while a second customer never had any problems with either one? Do you know what voltages the two customers were using?

However, you do seem to agree that the Terrasic cable doesn't have the overshoot problems that the Altera cable has?

Also, wouldn't using 2.5V levels on a 3.3V IO bank be a cause for TCK problems? Any dips or ringing would be much more likely to cross the threshold voltage and cause double-clocking or a poor duty cycle.